Effect of time scale on redox-driven ion and solvent transfers at nickel hydroxide films in aqueous lithium hydroxide solutions

Ion Dynamics at the Carbon Electrode/Electrolyte Interface: Influence of Carbon Nanotubes Types

Electrochemical quartz crystal microbalance (EQCM) and AC-electrogravimetry methods were employed to study ion dynamics in carbon nanotube base electrodes in NaCl aqueous electrolyte. Two types of carbon nanotubes, Double Wall Carbon Nanotube (DWCNT) and Multi Wall Carbon Nanotube (MWCNT), were chosen due to their variable morphology of pores and structure properties. The effect of pore morphology/structure on the capacitive charge storage mechanisms demonstrated that DWCNT base electrodes are the best candidates for energy storage applications in terms of current variation and specific surface area. Furthermore, the mass change obtained via EQCM showed that DWCNT films is 1.5 times greater than MWCNT films in the same potential range. In this way, the permselectivity of DWCNT films showed cation exchange preference at cathode potentials while MWCNT films showed anion exchange preference at anode potentials. The relative concentration obtained from AC-electrogravimetry confirm that DWCNT base electrodes are the best candidates for charge storage capacity electrodes, since they can accommodate higher concentration of charged species than MWCNT base electrodes.

Tracking the interfacial charge transfer behavior of hydrothermally synthesized ZnO nanostructures via complementary electrogravimetric methods

The mechanism of species fluxes during the charge-discharge process in a nanostructured ZnO electrode was studied by a combined methodology of electrochemical quartz-crystal microbalance (EQCM) and ac-electrogravimetry. Under the conditions of this study, anions (SO42-) possess the highest kinetics to be transferred at the electrode/electrolyte interface in the charge balance while cations (identified as Na+·5H2O and Na+) play the major role as charge carriers. Free H2O molecules present a sluggish behavior and their interfacial transfer occurs at a low scan rate or low frequencies. These findings shed light on the nature of ions and solvent participation in the charge balance of hydrothermally synthesized ZnO nanostructures directly grown on a QCM device. The combined methodology proposed herein provides dynamic and gravimetric analysis of interfacial charge transfer and can be extended to investigate other nanostructured metal oxide-based electrodes for energy storage.

Ion intercalation dynamics of electrosynthesized mesoporous WO3 thin films studied by multi-scale coupled electrogravimetric methods

Mesoporous WO₃ thin films were prepared electrochemically by using an ionic surfactant during the synthesis, and the electrochemical properties are investigated in comparison with their dense analogues.